dgb: RE-LAND sharechain verify+tracker (recover orphaned #116 slice-2)

[frstrtr]

Recovers commit 534aa5f (share_check + share_tracker), orphaned when #116 auto-closed unmerged after its base branch dgb/pool-layer-port was --delete-branch'd on the #115 merge. Re-landed on current master (now contains #112 + #115).

Commits

• bb3026e faithful re-land of 534aa5f (cherry-pick, clean, no conflicts) — share_check.hpp + share_tracker.hpp, Scrypt-only sharechain verify+tracker
• a6bfe37 add to share_tracker.hpp (self-contained-include fix, mirrors btc/share-tracker-cstdint)

Oracle reconciliation (per integrator request)

Verified share_check/share_tracker against the new DGB oracle (frstrtr/p2pool-dgb-scrypt):

• Both files hardcode ZERO consensus bytes. IDENTIFIER, PREFIX, donation script, address versions, PoW func, max_target are ALL pulled at runtime from core::CoinParams (params.active_identifier_hex(), params.donation_script_func(), params.address_version, params.pow_func, ...).
• The oracle bytes (IDENTIFIER 4b62545b1a631afe / PREFIX 1c0553f23ebfcffe / donation forrestv P2PK / minproto 1700/3301) live in config_pool.hpp, owned by the separate held dgb/oracle-switch-consensus branch (c6b5fed). These files consume them — no divergence to fold in at this layer.
• MERGED_KEY_PREFIX ("MERGED:") is the version-neutral sharechain weight-map DB key, matches p2pool merged format.

Status

• Both headers pass standalone -fsyntax-only against current master headers.
• Headers remain dormant (not yet compiled by any target) until ci-steward wires the OBJECT-lib; the cstdint fix makes share_tracker self-contained for that wiring.
• HOLD merge — integrator merges on operator push approval.